I kind of think that one of the most representative images from Capaldi’s run as the Doctor is the Doctor, holding a Dalek’s gun with one hand, with the other holding the hand of a child who is holding the Doctor’s screwdriver and will grow up to be his enemy, and taking that child home.
Kindness. Mercy. Compassion. Even when it’s hard. Even when there won’t be any type of reward for it. Always mercy. Always compassion. Just because it’s kind. Just because it’s the right thing to do.